Optical scanning apparatus, an image formation apparatus, and a phase modulation method

Abstract

An optical scanning apparatus, an image formation apparatus, and a phase modulation method are disclosed. The optical scanning apparatus includes a liquid crystal device for deflecting an optical beam irradiated by a semiconductor laser. The driving voltages for the liquid crystal device are controlled based on, e.g., the temperature of the liquid crystal device so that degradation of the diameter of a spot of the optical beam due to wavefront aberration is prevented.

1. An optical scanning apparatus wherein a scanned surface is scanned by an optical beam irradiated from a luminous source, comprising:
 a liquid crystal device for deflecting an optical path of the optical beam by generating a potential gradient at an electrode pattern having a strip form, said electrode pattern including a plurality of transparent electrode components aligned in one direction and connected to each other through a resistor, the potential gradient being generated by applying a first driving voltage to the transparent electrode component at an end row of the electrode pattern and a second driving voltage to another end row of the electrode pattern; and 
 a wavefront aberration control unit for controlling an amount of wavefront aberration generated in the liquid crystal device by controlling a reference voltage that is a middle voltage between the first and second driving voltages based on a phase modulation characteristic of the liquid crystal device in response to the potential gradient generated by the first and second driving voltages. 
 
     
     
       2. The optical scanning apparatus as claimed in  claim 1 , wherein
 the wavefront aberration control unit controls the reference voltage according to a deflection angle of the optical beam. 
 
     
     
       3. The optical scanning apparatus as claimed in  claim 1 , further comprising:
 a beam waist position detecting unit for detecting a beam waist position of the optical beam; 
 wherein the wavefront aberration control unit controls the amount of the wavefront aberration based on a detection result of the beam waist position detecting unit. 
 
     
     
       4. The optical scanning apparatus as claimed in  claim 1 , further comprising:
 a temperature detecting unit for detecting temperature of the liquid crystal device; 
 wherein the wavefront aberration control unit controls the amount of the wavefront aberration based on a detection result of the temperature detecting unit. 
 
     
     
       5. The optical scanning apparatus as claimed in  claim 1 , further comprising:
 an optical system that generates a power component that moves a beam waist position of the optical beam away from the luminous source if the temperature of the liquid crystal device is lower than predetermined temperature, and moves the beam waist position of the optical beam closer to the luminous source if the temperature of the liquid crystal device is higher than the predetermined temperature so as to cancel a variation of the phase modulation characteristic of the liquid crystal device. 
 
     
     
       6. The optical scanning apparatus as claimed in  claim 5 , wherein
 a magnitude of the power component generated by the optical system takes a minimum value near a median of a working temperature range of the liquid crystal device. 
 
     
     
       7. The optical scanning apparatus as claimed in  claim 6 , wherein
 the reference voltage is set up such that a fluctuation of the beam waist position takes a minimum value near the median of the working temperature range of the liquid crystal device. 
 
     
     
       8. An image formation apparatus that forms an image based on a latent image formed on a scanned surface, comprising:
 the optical scanning apparatus as claimed in  claim 1  for forming latent image on the scanned surface; and 
 a processing unit for forming the image on the scanned surface based on the latent image formed by the optical scanning apparatus. 
 
     
     
       9. A phase modulation method of modulating a liquid crystal device that deflects an optical beam for scanning a scanned surface, wherein the liquid crystal device comprises an electrode pattern having a strip form, said electrode pattern including a plurality of transparent electrode components aligned in one direction and connected to each other through a resistor; the method comprising:
 a prediction step of predicting an amount of wavefront aberration produced when the optical beam is deflected by the liquid crystal device, wherein the prediction is based on a phase modulation characteristic of the liquid crystal device in response to a potential gradient generated by a first and second driving voltages; and 
 a control step of controlling the first driving voltage and the second driving voltage applied to the liquid crystal device based on the amount of the wavefront aberration predicted in the prediction step. 
 
     
     
       10. The phase modulation method as claimed in  claim 9 , wherein
 the prediction step predicts the amount of the wavefront aberration based on a temperature characteristic of a phase difference characteristic curve of the liquid crystal device, and a thermometry result of the liquid crystal device. 
 
     
     
       11. The phase modulation method as claimed in  claim 9 , wherein
 the prediction step predicts the amount of the wavefront aberration based on a beam waist position of the optical beam on the scanned surface. 
 
     
     
       12. The phase modulation method as claimed in  claim 9 , wherein
 the control step controls a reference voltage that is a middle voltage between the first driving voltage applied to the transparent electrode component at an end row of the electrode pattern and the second driving voltage applied to another end row of the electrode pattern.